Method of performing anterior cruciate ligament reconstruction using biodegradable interference screw

ABSTRACT

A method of replacing an ACL with a graft. The method provides for the drilling bone tunnels in a femur and a tibia. A replacement graft is provided having first and second ends. A biodegradable composite screw is provided. The screw is made from a biodegradable polymer and a bioceramic or a bioglass. At least one end of the graft is secured in a bone tunnel using the biodegradable composite screw.

TECHNICAL FIELD

The field of art to which this invention relates is surgical proceduresfor the repair of an anterior cruciate ligament, more specifically, asurgical procedure for affixing an anterior cruciate ligament graft intoa bone using a biodegradable interference screw.

BACKGROUND OF THE INVENTION

The knee joint is one of the strongest joints in the body because of thepowerful ligaments that bind the femur and tibia together. Although thestructure of the knee provides one of the strongest joints of the body,the knee may be one of the most frequently injured joints, e.g.,athletes frequently stress and tear knee ligaments. The large number ofligament injuries has given rise to considerable innovative surgicalprocedures and devices for replacing and reconstructing torn ordislocated ligaments, typically involving grafting autografts,allografts, or a synthetic construct, to the site of a torn ordislocated ligament. For example, the replacement of an anteriorcruciate ligament (ACL) may involve transplanting a portion of thepatellar tendon, looped together portions of semitendinosus-gracilis(hamstring) tendons, or donor Achilles tendons, to attachment sites inthe region of the knee joint.

Tears or ruptures of an anterior cruciate ligament of a knee (ACL)typically require a major surgical intervention wherein a replacementgraft is mounted to the ends of the bones surrounding the knee in orderto reconstruct the knee. A ruptured or damaged ACL typically results inserious symptoms such as knee instability resulting in diminishedability to perform high level or recreational sports, or in some casesdaily activities relating to motility. Although the use of knee bracesmay alleviate some of these symptoms, the potential long term effects ofa damaged ACL include meniscal damage and articular cartilage damage.

The basic steps in a conventional ACL reconstruction procedure include:harvesting a graft made from a portion of the patellar tendon withattached bone blocks; preparing the graft attachment site (e.g.,drilling holes in opposing bones of the joint in which the graft will beplaced); placing the graft in the graft attachment site; and rigidlyfixing the bone blocks in place within the graft site, i.e., the holesor “bone tunnels”. The screws used to fix the graft in place are called“interference screws” because they are wedged between the bone block andthe wall of the bone tunnel into which the bone block fits. Typically,there is very little space between the bone block and the inner wall ofthe bone tunnel in the bone at the fixation site.

Several types of surgical procedures have been developed to replace theACL. Although repair would be a preferred procedure, it is not typicallypossible since the end of the torn ACL is typically not of sufficientlength to reattach successfully. However, reconstructions can be made toa damaged ACL.

There are several types of conventional replacement grafts that may beused in these replacement procedures. In all procedures tibial andfemoral tunnels are drilled by the surgeon using conventionaltechniques. Known, conventional drill guides and drills are used. In onetype of procedure known as a bone-tendon-bone procedure, an autografttendon is harvested from the patellar tendon along with an attached boneblock on one end harvested from the patella and a harvested bone blockon the other end harvested from the tibia. In order to secure the graftin the knee, one end is mounted into the tibial tunnel and other end ismounted into the femoral tunnel. This is done by mounting the opposedbone blocks in the tibial and femoral tunnels, respectively, in thefollowing manner. A guide pin is passed through the tibial tunnel, intothe fermoral tunnel and out through the lateral femoral cortex. Sutureis used to attach the graft to the proximal end of the guide pin. Thedistal end of the guide pin is then pulled out of the lateral cortex ofthe femur and the graft is pulled into the knee (femoral and tibialtunnels). Once the bone blocks are emplaced in the respective tibial andfemoral tunnels, the blocks are secured in place in the followingmanner. One method of securing or fixing the ends of the graft in thetunnels is to use a conventional metallic interference screw. The screwis inserted into the opening of a tunnel and placed in between the graftand the interior surface of the bone tunnel. It is then turned andscrewed into the tunnels, thereby forcing the end of the graft againstan interior surface of the bone tunnel. The ends of graft are securedand maintained in place in the tunnel by means of a force fit providedby the interference screw.

Another surgical procedure for the replacement of an anterior cruciateligament involves providing a graft ligament without attached boneblocks. The graft can be an autograft or an allograft. The autograftsthat are used may typically be harvested from the hamstring tendons orthe quadriceps tendons. The allografts that are conventionally used areharvested from cadaveric sources, and may include the hamstring tendons,quadriceps tendons, Achilles tendon, and tibialus tendons. If desired,and if readily available, it may possible to use synthetic grafts orxenografts. Tibial and femoral tunnels are similarly drilled in thetibia and femur respectively using-conventional techniques, drill guidesand drills. Once the tunnels have been drilled, the surgeon then pullsthe graft through the tibial and femoral tunnels using conventionaltechniques such that one end of the graft resides in the tibial tunneland the other end of the graft resides in the femoral tunnel. Forexample, one conventional technique for pulling a graft through thetunnels is to attaché the graft to the proximal end of a guide pin usingconventional surgical suture. The guide pin is then passed through thetibial tunnel, into the femoral tunnel, and out though the femoralcortex. The distal end of the guide pin is then pulled out of thelateral cortex of the femur and the graft is pulled into the knee(femoral and tibial tunnels). After the surgeon has emplaced andpositioned the ends of the graft in the respective tunnels, the graftends need to be secured and fixed in place to complete the replacementprocedure. One method of securing or fixing the ends of the graft in thetunnels is to use a conventional metallic interference screw. The screwis inserted into the opening of a tunnel and placed in between the graftand the interior surface of the bone tunnel. It is then turned andscrewed into the tunnels, thereby forcing the end of the graft againstan interior surface of the bone tunnel. The ends of the graft aresecured and maintained in place in the tunnel by means of a force fitprovided by the bone screw.

Interference screws for anchoring ligaments to bone are typicallyfabricated from medically approved metallic materials that are notnaturally degraded by the body. One potential disadvantage of suchscrews is that once healing is complete, the screw remains in the bone.An additional disadvantage of a metal screw is that in the event of asubsequent rupture or tear of the graft, it may be necessary to removethe metal screw from the bone site. Metallic screws may include athreaded shank joined to an enlarged head having a transverse slot orhexagonal socket formed therein to engage, respectively, a similarlyconfigured, single blade or hexagonal rotatable driver for turning thescrew into the bone. The enlarged heads on such screws can protrude fromthe bone tunnel and can cause chronic irritation and inflammation ofsurrounding body tissue.

Permanent metallic medical screws in movable joints can, in certaininstances, cause abrading of ligaments during normal motion of thejoint. Screws occasionally back out after insertion, protruding intosurrounding tissue and causing discomfort. Furthermore, permanentmetallic screws and fixation devices may shield the bone from beneficialstresses after healing. It has been shown that moderate periodic stresson bone tissue, such as the stress produced by exercise, helps toprevent decalcification of the bone. Under some conditions, the stressshielding which results from the long term use of metal bone fixationdevices can lead to osteoporosis.

Biodegradable interference screws have been proposed to avoid thenecessity of surgical removal after healing. Because the degradation ofa biodegradable screw occurs over a period of time, support load istransferred gradually to the bone as it heals. This reduces potentialstress shielding effects.

In order to overcome the disadvantages that may be associated with metalinterference screws, interference screws made from biodegradablepolymers are known in this art. For example, it is known to use aninterference screw made from polylactic acid. Ideally, the biodegradableinterference screw will rapidly absorb or break down and be replaced bybone. However, it is known that screws made from polylactic acid tend tomaintain their structural integrity for very long periods of timethereby preventing the desired bone in growth. Attempts have been madeto improve the bone regeneration process by using other biodegradablepolymers and copolymers of lactic acid that resorb or absorb morequickly. The problem often associated with these quicker absorbingpolymers or copolymers is that the bone regeneration may proceed at amuch slower rate than the rate of resorption, resulting in prematuremechanical failure of the screw and a resulting pull out of the graftend from the femoral tunnel. Some of the absorbable interference screwsof the prior art may take several years to absorb, and may result in afibrous tissue mass or cyst being left behind, not bone. This lack ofbone in-growth may create fixation problems if the ACL is torn again,necessitating a new graft replacement. In addition, if the screw absorbstoo slowly, the screw will need to be removed in the event of asubsequent failure of the graft.

Accordingly, what is needed in this art is a novel method of performingan ACL replacement graft procedure using a novel interference screw madefrom a biodegradable material which rapidly absorbs or degrades andpromotes bone in-growth.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a novelmethod of replacing a ruptured or injured anterior cruciate ligamentwith a graft using a novel biodegradable interference screw consistingof a composite of a biodegradable polymer and a biodegradable ceramic orbioglass.

Accordingly, a novel method of repairing an anterior cruciate ligamentin the knee is disclosed. A replacement graft is provided having a firstend and a second end. A bone tunnel is drilled in the tibia. A bonetunnel is also drilled in the tibia. The first end of the graft ismounted in the femoral bone tunnel. The second end of the graft ismounted in the tibial bone tunnel. A biodegradable, compositeinterference screw is provided. The interference screw is made from acopolymer of poly (lactic acid) and poly(glycolic acid) and abioceramic. The biodegradable screw is inserted into the femoral bonetunnel between an interior surface of the femoral bone tunnel and thefirst end of the graft. The interference screw is rotated such that thescrew is substantially contained within the femoral bone tunnel, and thefirst end of the graft is fixed in place between the interference screwand a section of the interior surface of the femoral bone tunnel.

These and other features, aspects and advantages of the presentinvention will become more apparent from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a biodegradable interference bone screw usefulin the method of the present invention.

FIG. 1B is an end view of the interference bone screw of FIG. 1A.

FIG. 1C is a cross-sectional view of the inference bone screw of FIG. 1Btaken along view line A-A.

FIG. 2 is a side view of a driver device useful for emplacing the bonescrew of FIG. 1 in a bone tunnel.

FIG. 3 illustrates a bone-tendon-bone graft prior to emplacement in aknee for an ACL reconstruction.

FIG. 4 shows a guide wire placed into the femoral tunnel between thetunnel wall and the bone block.

FIG. 5 illustrates a conventional tap being used to tap a hole betweenthe wall and the bone block.

FIG. 6 shows a biodegradable interference screw being inserted into thefemoral tunnel between the tunnel wall and the bone block.

FIG. 7 illustrates a guide wire placed into the tibial tunnel betweenthe tunnel wall and the bone block.

FIG. 8 illustrates a conventional tap device being used to tap a holebetween the tunnel wall and the bone block.

FIG. 9 illustrates the screw being inserted into the tibial tunnelbetween the tunnel wall and the bone block.

FIG. 10 is a side view of the knee after the ACL replacement procedurehas been completed.

FIG. 11A is a histological section of a PLA/PGA bone pin containingβ-tricalcium phosphate and surrounding tissue.

FIG. 11B is a histological section of a PLA bone pin and surroundingtissue.

FIG. 11C is a histological section of a PLA bone pin and surroundingtissue.

FIG. 11D is a histological section of a PLA bone pin containingβ-tricalcium phosphate and surrounding tissue.

FIG. 11E is a histological section of a PLA/PGA bone pin containingβ-tricalcium phosphate and surrounding tissue.

DETAILED DESCRIPTION OF THE INVENTION

The novel interference screws of the present invention are a compositeof a biodegradable polymer or copolymer and a bioceramic. The termbiodegradable as used herein is defined to mean materials that degradein the body and then are either absorbed into or excreted from the body.The term bioceramic as defined herein is defined to mean ceramic andglass materials that are compatible with body tissue. The bioceramicsare preferably biodegradable.

The biodegradable polymers that can be used to manufacture the compositescrews used in the novel process of the present invention includebiodegradable polymers selected from the group consisting of aliphaticpolyesters, polyorthoesters, polyanhydrides, polycarbonates,polyurethanes, polyamides and polyalkylene oxides. Preferably, thebiodegradable polymers are aliphatic polyester polymers and copolymers,and blends thereof. The aliphatic polyesters are typically synthesizedin a ring opening polymerization. Suitable monomers include but are notlimited to lactic acid, lactide (including L-, D-, meso and D,Lmixtures), glycolic acid, glycolide, ε-caprolactone, p-dioxanone(1,4-dioxan-2-one), trimethylene carbonate (1,3-dioxan-2-one),δ-valerolactone, and combinations thereof. These monomers generally arepolymerized in the presence of an organometallic catalyst and aninitiator at elevated temperatures. The organometallic catalyst ispreferably tin based, e.g., stannous octoate, and is present in themonomer mixture at a molar ratio of monomer to catalyst ranging fromabout 10,000/1 to about 100,000/1. The initiator is typically an alkanol(including diols and polyols), a glycol, a hydroxyacid, or an amine, andis present in the monomer mixture at a molar ratio of monomer toinitiator ranging from about 100/1 to about 5000/1. The polymerizationtypically is carried out at a temperature range from about 80° C. toabout 240° C., preferably from about 100° C. to about 220° C., until thedesired molecular weight and viscosity are achieved. It is particularlypreferred to use a copolymer of poly(lactic acid) and poly(glycolicacid). In particular, a copolymer of about 85 mole percent poly(lacticacid) and about 15 mole percent poly(glycolic acid).

The bioceramics that can be used in the composite screws used in thenovel process of the present invention include ceramics comprisingmono-, di-, tri-, α-tri-, β-tri-, and tetra-calcium phosphate,hydroxyapatite, calcium sulfates, calcium oxides, calcium carbonates,magnesium calcium phosphates. It is particularly preferred to use aβ-tritricalcium phosphate.

In addition to bioceramics, bioglasses may also be used in the compositescrews. The bioglasses may include phosphate glasses and bioglasses.

The amount of the bioceramic or bioglass in the composite interferencescrew will be sufficient to effectively promote bone in-growth.Typically the amount will be about 2.0 Vol. % to about 25.0 Vol. %, andpreferably about 15.0 Vol. %.

The composite, biodegradable interference screws useful in the presentinvention are manufactured in conventional extrusion and moldingprocesses using conventional extruding and molding equipment. In atypical process, dry biodegradable polymer pellets and dry bioceramic orbioglass are metered into a conventional heated screw extruder. Thematerials are heated and blended in the extruder for a sufficientlyeffective residence time to provide a viscous composite having a uniformdistribution of the particles of bioglass or bioceramic. Then theviscous composite is cooled and chopped to form pellets of thehomogenous composite. The interference screws may be molded in aconventional injection molder. In a typical injection molder, pellets ofcomposite are fed into a barrel, passed through a heating zone to meltthe polymer, then pushed forward through a nozzle and into the cavity ofa chilled mold. After cooling, the mold is opened, and the part isejected.

A biodegradable interference screw 5 of the present invention is seen inFIGS. 1A-C. The screw 5 is seen to have an elongate body 10 having acannulated passage 20 therethrough, with proximal socket opening. 22 anddistal opening 26. The body 10 is seen to have a plurality of threadflights 30 extending from the outer surface 12. The body 10 is seen tohave distal end 14 and proximal end 16. A driver 50 for inserting oremplacing the crew 5 in a bone tunnel is seen in FIG. 2. The driver 50has an elongated rod member 60 having distal end 62 and proximal end 64.Distal end 62 is seen to have a driver 63 extending therefrom having ahexagonal configuration for mating with socket 22. The screw 5 ismounted to driver 50 by inserting the driver 63 of distal end 62 intothe mating proximal socket end 22 of the passage 20.

The biodegradable composite interference screws described herein areused in the novel ACL reconstruction procedure of the present inventionin the following manner as illustrated if FIGS. 3-10. Prior toreconstructing the ACL using a bone-tendon-bone graft, a patient isprepared for surgery in a conventional manner. The patient's knee 100 isprepared for surgery in a conventional manner including swabbing theskin around the knee with a conventional antiseptic solution, anddraping the knee. The knee 100 is then angulated by the surgeon in aconventional manner to facilitate the surgical procedure. The patient isthen anesthetized in a conventional manner using conventionalanesthetics, either general or local at the discretion of the surgeon.As seen in FIG. 1, the knee 100 is seen to have a femur 150 having adistal end 160 and a tibia 130 having a proximal end 140. Proximal end140 is seen to have a tibial plateau 141. Extending from the distal end160 of femur 150 are the femoral condyles 170 separated by notch 175.For the sake of illustration, the tendons, cartilage, fascia, softtissue and skin are not shown. The knee 100 is accessed by the surgeonusing a conventional arthroscope that is inserted though a conventionalcannula, that has been previously emplaced in the knee 100 in aconventional manner through an incision in the skin covering the knee100. A flow of sterile saline is initiated through channels in thearthroscope into the knee 100. The stumps of the ACL are removed fromthe surfaces of the tibial plateau 141 and the chondryl notch 175 usingconventional shavers that are inserted through the cannula. Abone-tendon-bone graft 200 is harvested and prepared by the surgeon in aconventional manner. The graft 200 is harvested by making an incision inthe skin over the knee 100 down the anterior patella to the tibial. Aconventional sagittal saw is then used to harvest the opposed bone plugs220 that are connected by harvested patellar tendon segment 210. Thetendon segment 210 is cut from the patellar tendon in a conventionalmanner using a scalpel. If desired, a graft without bone blocks attachedmay also be used in the method of the present invention.

The procedure continues by mounting a conventional tibial drill guide(not shown) to the proximal end of the tibia 130. A conventional guidepin 250 is inserted into the drill guide and mounted to a conventionalsurgical drill. The guide pin 250 is seen to have elongated body 252having distal cutting end 254 and proximal end 255 with suture mountingopening 257. The guide pin 250 is drilled into the front of the tibia130 in a conventional manner until the distal end 254 exits out from thetibial plateau 141. The drill guide is then removed from the tibia 130and a conventional surgical reamer is placed over the guide pin 250 andturned to ream out a tibial tunnel 280 having a passage 282, an innertunnel wall 283, a top opening 284 out of the tibial plateau 141 and abottom opening 286 out through the tibia 130. Then the reamer and theguide pin 250 are removed from the tibial tunnel 280 and a conventionalfemoral aimer device (not shown) is inserted into tibial tunnel 280 andmanipulated until the distal end of the femoral aimer engages theappropriate location on the femoral notch 175. Then the guide pin 250 isinserted through a passage in the femoral aimer, and the guide pin 250is mounted to a conventional surgical drill and drilled into the femoralnotch such that the distal end exits out through the lateral side of thefemur 150 and through the skin overlying that section of the femur 150.Next, the femoral aimer is removed from the knee 100 and a conventionalsurgical bone reamer is placed over the guide pin 250 and moved throughthe tibial tunnel 280, and a femoral tunnel 290 is drilled though thefemur having a passage 292, an inner tunnel wall 293, an upper opening294 out through the lateral side of the femur 130 and a bottom opening296 out of the femoral notch 175. The reamer is then removed from thebone tunnel 290.

Referring to FIG. 3, the graft 200 is illustrated proximal to the knee100 having the tibial tunnel 280 and femoral tunnel 290 drilled andreamed in the tibia 130 and femur 150, respectively. The guide pin 250is seen to reside in the knee 100 with the elongated body 252 of guidepin 250 substantially contained within tibial tunnel 280 and femoraltunnel 290, with distal end 254 exiting out through opening 294 andproximal end 255 exiting out from opening 286. Next, the surgeon threadssutures 230 through the suture tunnels 222 in bone blocks 220. Thesuture through the top bone block 220 is also threaded through opening257 of guide pin 250. The surgeon then pulls guide pin 250 distally suchthat the graft 200 is displaced into the knee 100 with upper bone graft220 located in passage 292 of femoral tunnel 290 and lower bone block220 located in passage 282 of tibial tunnel 280. An optional step oftapping the bone block and boned tunnel is illustrated in FIGS. 4 and 5.A guide wire 300 is seen to be inserted into femoral bone tunnel 290between bone block 220 and inner tunnel wall 293. Then, a conventionalcannulated bone tap 310 is inserted over guide wire 300. The bone tap310 has elongated cannulated member 310, having a transverse handle 314mounted to proximal end 312 and a tapping/cutting end 318 mounted todistal end 316. The tapping cutting end 318 is rotated by rotatinghandle 314, causing an opening to be cut and threads to be tappedbetween inner wall 293 and bone block 220 in the femoral tunnel 290.Then, as seen in FIG. 6, a biodegradable interference screw 5 mounted toa driver 50 is mounted to the guide wire 300 and threaded into thefemoral tunnel 290 between the bone block 220 and the inner wall 293,thereby securing the upper bone block 220 in the passage 292 of femoraltunnel 290. The guide wire is then removed from the femoral tunnel 290and inserted into opening 286 of and into passage 280 of tibial tunnel280 between the lower bone block 220 and the inner wall 183 as seen inFIG. 7. Then, the surgeon tensions the graft 200 by pulling proximallyon sutures 230 connected to lower bone block 220. Then, the bone tap 310is inserted into tibial tunnel 280 over the guide wire 300 and anopening and threads are cut and tapped between inner wall 283, and boneblock 220. Finally, the bone tap 310 is removed and as seen in FIG. 9, abiodegradable interference screw 5 is mounted over the guide wire 300and threaded into the tibial tunnel 280 between inner wall 282 and lowerbone block 220, thereby securing the lower bone block 220 in tibialtunnel 280. This completes the ACL reconstruction, and the graft 200 isnow secured in the knee 100. The complete reconstructed knee 100 is seenin FIG. 10. The surgeon then checks the knee for proper flexion andcompletes the procedure in a conventional manner by removing the scopeand portal, and conventionally closing and/or suturing and bandaging allincisions.

The following examples are illustrative of the principles and practiceof the present invention although not limited thereto.

EXAMPLE 1

Biodegradable composite bone pins 1 were prepared in a conventionalmanner and into the femurs of mammalian laboratory animals. The pinswere of the following three compositions: A) composites of 15/85% byvolume β-tricalcium phosphate and (85/15)poly (lactide co-glycolide); B)poly(lactide); and C) composite of 15%/85% by volume β-tricalciumphosphate and poly(lactide). About 24 months after implantation, theanimals were euthanized and histological sections were obtained. As seenin FIG. 11A, a bone pin 500 having a Composition (A) demonstrated asignificant degree of absorption when compared with the originaldiameter indicated by arrows 505, and significant tissue (bone)in-growth. In addition, minimal tissue reaction was observed. As seen ifFIGS. 11B and 11C, bone pins 510 and 520 having Composition (B)exhibited minimal absorption compared with the original diametersindicated by arrows 515 and 525, respectively. As seen in FIG. 11D, abone pin 530 having Composition C showed minimal absorption comparedwith the original diameter indicated by arrows 535. And, as seen in FIG.11E, a bone pin 540 having Composition A demonstrated a significantdegree of absorption compared with the original diameter indicated byarrows 545, and significant tissue (bone) in-growth. Minimal tissuereaction was observed.

The novel ACL graft replacement method of the present invention using acomposite interference screw made from a bioaborbable polymer and abioceramic or bioglass has many advantages. The advantages includehaving improved bioabsorption and bone replacement, improved tissuein-growth, and minimizing tissue trauma. In addition, there is anoptimal balance between stiffness and elasticity of the screws.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

1. A method of replacing an anterior cruciate ligament in a knee,comprising: providing a graft having a first end and a second end;drilling a bone tunnel in a tibia, said bone tunnel having an innerwall; drilling a bone tunnel in a femur, said bone tunnel having aninner wall; mounting the first end of the graft in the femoral bonetunnel; mounting the second end of the graft in the tibial bone tunnel;providing a biodegradable, composite interference screw, saidinterference screw comprising: a biodegradable comprising a copolymer ofpoly (lactic acid) and poly(glycolic acid); and, a bioceramic; insertingthe biodegradable screw into the femoral bone tunnel between an interiorsurface of the femoral bone tunnel and the first end of the graft; and,rotating the interference screw such that the screw is substantiallycontained within the femoral bone tunnel, and the first end of the graftis fixed in place between the interference screw and a section of theinterior surface of the femoral bone tunnel.
 2. The method of claim 1,additionally comprising the steps of: inserting the second end of thegraft into the tibial tunnel; inserting the biodegradable screw into thetibial bone tunnel between an interior surface of the tibial bone tunneland the second end of the graft; and, rotating the interference screwsuch that the screw is substantially contained within the tibial bonetunnel, and the second end of the graft is fixed in place between theinterference screw and a section of the interior surface of the tibialbone tunnel.
 3. The method of claim 1, wherein the bioceramic comprisesa bioceramic selected from the group consisting of mono-, di-, tri,α-tri, β-tri and tetra-calcium phosphate, hydroxyapatite, calciumsulfates, calcium oxides, calcium carbonate, and magnesium calciumphosphates.
 4. The method of claim 4 wherein the bioceramic comprisesβ-tricalcium phosphate.
 5. The method of claim 1 wherein thebioabsorbable polymer comprises a copolymer of polylactic acid and poly(glycolic acid) comprising about 85 mole percent to about 95 molepercent of poly (lactic acid) and about 5 mole percent to about 15 molepercent of poly (glycolic acid).
 6. The method of claim 5 wherein thebioabsorbable polymer comprises a co-polymer of about 85 mole percentpoly (lactic acid) and about 15 mole percent poly (glycolic acid). 7.The method of claim 1 wherein the composite screw comprises about 2.0Volume percent to about 25.0 Volume percent of bioceramic.
 8. The methodof claim 1, wherein the composite screw comprises about 15.0 Volumepercent of bioceramic.
 9. The method of claim 1, wherein the graft has abone block attached to one end.
 10. The method of claim 1, wherein eachend of the graft has a bone block attached thereto.
 11. The method ofclaim 1 comprising the additional step of tapping the inner surface ofthe bone tunnels and the bone blocks to create a threaded spacetherebetween.